The invention relates to a vehicle drive unit of the type having a reciprocating piston engine, a transmission, and a transmission output shaft. The engine sound generating parts are enclosed in an engine casing. Such a drive unit is known from German published unexamined patent application (DOS) No. 2,612,182. Although the entire driving mechanism carrier is suspended in a structure-borne noise isolated manner in the noise capsule in this known drive unit, the disadvantage is that the transmission casing is rigidly connected to the noise capsule so that the transmission noises and the noises originating from the output shaft outside the transmission are transmitted to the noise capsule which can thus only incompletely fulfill its task of sound insulation. In addition, the sound insulation of the driving mechanism carrier requires the crankshaft and transmission input shaft to be separated in the known drive unit, which separation is achieved by an elastic coupling inserted between them. However, this requires considerable installation space especially in a location in which in most cases, such as, for example, in a motor vehicle, there are very restrictive space conditions.
An object of the invention is to construct the known drive unit in such a manner that transmission of structure-borne noise to the noise capsule is presented even with a continuous metallic connection between the crankshaft and the transmission shaft.
In a drive unit of the type initially mentioned, this object is achieved by providing that the sound insulating engine casing also encloses the transmission and transmission casing.
Since any metallic connection between the transmission casing and the noise capsule is avoided in the drive unit constructed in accordance with the invention, the transmission of sound between these two and the radiation of sound from the transmission casing to the outside is avoided overall without requiring a flexible coupling between the crankshaft and the transmission shaft or an encapsulation which is remote from the engine.
Constructing the drive unit, in especially preferred embodiments, with the transmission output shaft connected via a flexible shaft coupling to a further output shaft, suppresses the transmission of sound generated in the internal combustion engine or the transmission via the output shaft to the outside, the flexible coupling being arranged at a location which provides sufficient space.
The construction of the drive unit in certain preferred embodiments with an elastic support assembly connecting the crankshaft and transmission output shaft at the engine casing noise capsule, offers the advantage of supporting the output shaft in the noise capsule which completely closes the latter off towards the outside but, at the same time, allows relative movements between the output shaft and the noise capsule. In especially preferred embodiments with a toothed elastic ring coupling, a better compound effect between the support rings and the elastic ring layer which provides the possibility of increased carrying capability of the support is obtained.
Due to the construction of especially preferred embodiments of the drive unit, with a skeleton type transmission and the transmission casing constructed as a support frame, resultant increases in weight can be avoided by reducing the dimensions of the transmission casing to form a support frame carrying the transmission shafts since the tasks of the transmission casing as outside shielding and oil container can be taken over by the noise capsule in the drive unit according to the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.